Manifold solutions are available on the market for the insulation of mechanical equipment, such as in commercial and residential construction as well as industrial applications and the oil and gas industry.
Insulation products applied to heating and plumbing, HVAC (Heating, Ventilation and Air Conditioning) ducts and systems for commercial construction in non-residential buildings (such as hospitals, hotels and offices) as well as residential construction are mainly based upon polymeric foams. Light and heavy industry increase the use of such foams in plants, technical engineering facilities, trains and ships primarily for refrigeration, HVAC ducts and systems, coolants distribution and steam transportation equipment.
The reasons for choosing such materials are manifold: They are watertight and therefore prevent corrosion under insulation, have excellent thermal and acoustic insulation properties and they are easy to apply due to their flexibility, easy cuttability and bondability with one-component adhesives.
The polymeric insulation foams used for such applications comprise mainly two groups of materials, flexible elastomeric foams (FEFs) and polyethylene foams (PEFs).
Flexible elastomeric foams (FEFs) are flexible insulation materials with a high filler loading, achieved by a chemical expansion (foaming) process. Such materials are almost exclusively based on a narrow selection of polymer (elastomer) bases. The majority of such expanded materials are based upon NBR or NBR/PVC (e.g. NH/Armaflex®, AF/Armaflex®, K-Flex® ST, Kaiflex® KKplus) and EPDM (e.g. HT/Armaflex®, Aerocel® AC). Expanded EPDM is mainly used for higher temperature insulation, e.g. solar applications, whereas NBR is the most widespread polymer base for standard FEFs, such as in heating and plumbing and ventilation and cooling applications.
Due to the high loadings feasible with such materials, the product properties can be modified in a wide range, e.g. concerning flame resistance, thermal conductivity, mechanical properties, water vapour resistance etc. A disadvantage of such high loading is the higher density (>50 kg/m3) compared to other polymeric foams (e.g. LDPE foams: 25 kg/m3; Extruded polystyrene foams (XPS foams): 30 kg/m3). In addition, the manufacturing of FEFs requires an additional kneading/mixing step previous to extrusion of the compound.
The second group of insulation materials, called polyethylene foams (PEFs), is made by physical expansion (foaming), using physical blowing agents. Such materials comprise a very low level of fillers on account of the fact that fillers lead to an overnucleation and therefore a collapse of the material. Due to the limited possibilities of loading such materials with fillers, plasticizers, etc., the possibilities of modifying their properties are very limited. Therefore, the flexibility of PEFs in comparison to FEFs is worse, leading to several disadvantages, e.g. due to a significantly higher amount of cuttings during installation, which is a drawback in terms of installation time and costs. In addition, the adhesion of PE (polyethylene) is in general difficult due to its low polarity, leading again to drawbacks in comparison to FEFs.
Besides, PEFs need a storage time of several weeks for outgassing the (usually flammable) blowing agents, while FEFs can theoretically be used directly after production. Last but not least, PEFs are only available as tubes, insulation sheets comparable to FEFs are not commercially available (FEF sheets: AF/Armaflex®: 3-50 mm; Kaiflex® KKplus: 3-50 mm). This is mainly caused by the low flexibility and therefore impossibility to bend and glue it around tubes, vessels, tanks, etc.
Several approaches were made to improve PEFs to create properties comparable to commercially available FEFs, especially concerning flexibility, adhesiveness and flame resistance/smoke suppression.
Some commercially available PEFs achieve a BL-s1, d0 flame resistance classification according to EN 13501-1 (“SBI-Test”) for tubes (e.g. Climaflex© from NMC), which is the best classification that can be achieved with organic materials. Unfortunately, such classification is limited to a wall thickness up to 13 mm. A wall thickness of 20 and 25 mm achieves only a CL-s1, d0 classification.
The reason for such differences is obvious: The low filling capacity (limited by the aforementioned overnucleation) leads to a material comprising more than 95% of organic, which means flammable substances. Increasing the wall thickness of the material within the fire test (e.g. EN 13501-1) significantly increases the amount of flammable substances, leading to a drop in the fire classification (from B to C). This means, that the flame resistance of such materials can only be achieved with low densities and limited wall thicknesses. However, such low wall thickness are of declining interest for the current demands concerning insulation thickness, e.g. according to the German EnEV (Energie-Einspar-Verordnung).
Such a drop in fire classification also leads to another risk using such materials: Density variations can easily lead to a drop in the fire classification and the use of large quantities of such insulation materials entails the risk of a fire.
Such a risk does not exist when using FEFs, e.g. Armaflex© Ultima. That material has a BL-s1, d0 classification for the whole product range (9-25 mm wall thickness). The reason for such differences is based upon the significantly higher loading that is possible for such a product. Modifications of fire resistance are feasible in a wider range using fillers, flame retardants, additives, etc. Variations in densities therefore also have a negligible effect on flame resistance.
The poor flexibility of PEFs is another important drawback of such products. Several attempts were made to develop products with improved bendability and elasticity. EP1336064 claims a thermal insulation polyethylene foam comprising metallocene polyethylene with improved flexibility. Unfortunately, the composition needs to comprise at least 77% of metallocene polyethylene, which is significantly more expensive than common non-metallocene low density PEs (LDPEs) used for PEFs. Furthermore, the flexibility of such foams is still not comparable to FEFs. Similarly EP1645589 describes a flexible cross-linked polyethylene foam which is modified by metallocene polyethylene. Beside metallocene PE, ethylene copolymers may be used to further improve the flexibility of such foams (for example U.S. Pat. No. 6,872,756, CA2230093 and U.S. Pat. No. 5,059,631). Unfortunately, such copolymers either have a high copolymer (VA, vinyl acetate) content and therefore a negative impact on temperature resistance (ethylene-vinyl acetate (EVA) with VA content of 40 wt % (percent by weight): Tg<50° C.) or have a low copolymer content and therefore a very limited or almost no impact on the flexibility of the resulting foam (e.g. VA content of 15 wt %: Tg<90° C., Vicat softening point<70° C.). Moreover, even such materials with a low VA content decrease the overall temperature resistance.
Other ethylene copolymers show a comparable temperature behaviour like EVA, therefore such approaches either significantly decrease the temperature resistance and/or have almost no impact on flexibility of the resulting foam.
Beside polyolefin based polymers and copolymers, also styrene containing thermoplastic elastomers have been used to obtain softer foams. For example EP1795552, U.S. Pat. Nos. 6,653,360 and 9,260,578 describe a polyolefin based foam which is modified with a styrene-elastomer block copolymer and a plasticizer oil. The plasticizer oil is required to process the styrene-elastomer with the polyolefin and only a low amount of filling is possible. US2015/0225526 on the other hand describes a soft foam based on linear low density polyethylene (LLDPE) and an additional polymer which improves flexibility.
The disadvantage of all the prior teaching is the poor flame resistance, relatively high cost due to limitations in filling capability, significantly higher densities (excluding the material for application as an insulation foam), the use of plasticizers (drawbacks regarding migration, flammability, etc.) and the discontinuous shaping, crosslinking and foaming process.
Physically foamed and highly filled polypropylene based foams have been widely described in prior art (EP1449868, EP1512713 and U.S. Pat. No. 8,846,774), however no-one has managed until now to combine chemical foaming and coinciding crosslinking of highly filled and fire retardant polyethylene and TPE-s compounds for low density foams. US2016009885 and U.S. Pat. No. 6,110,985 describe highly filled polyolefin and rubber foams using chemical blowing agents, but their work indeed shows that achieving low densities is challenging. Even though the densities are not mentioned, the amount of chemical blowing agent (<10%) that is used is far too low to achieve densities as low as presented in this invention.